This invention relates to an electrostatic clutch operable by the Johnsen-Rahbek effect.
The Johnsen-Rahbek effect refers to electrostatic adhesion between the surface of an electrically conducting member and a closely adjacent surface of a semiconductive member under an applied voltage. This effect and application thereof are well known, and are described in the literature, e.g., in Fitch, C. J., "Development of the Electrostatic Clutch" IBM Journal of Research and Development, Volume I, January, 1957 page 49 et seq., and in Stuckes, A. D., "Some Theoretical and Practical Considerations of the Johnsen-Rahbek Effect" Proceedings I.E.E., Volume 103, Part No. 8, Mar. 1956 page 125 et seq.
Although a clutch operable by the Johnsen-Rahbek effect is favored by the development of relatively high mechanical forces using only low levels of input control energy, problems of wear and heat generation present formidable barriers to this utilization of the Johnsen-Rahbek effect.
Various attempts have been made to overcome or compensate for these problems. For example, U.S. Pat. No. 2,850,908, issued Sept. 9, 1958 describes a particular mechanical arrangement utilizing a pivoted lever having arms of unequal lengths in order to minimize wear and heating at the position at which maximum friction would normally occur. U.S. Pat. No. 3,871,944, issued Mar. 18, 1975 describes an integral laminar composite semiconductive element which may be used in electrostatic clutch or break devices in which a layer of semiconductive particles and a layer of metal particles are integrated with and bonded together by a hard non-conductive thermoset bonding resin; among the materials that may constitute the semiconductive particles described therein are silicon carbide, limestone, slate, barium titanate, etc., with phthalein-fluoran polymers being described as the preferred semiconductive material.
While the problems of wear and heat generation have been somewhat alleviated by such means, a continuing need for improved devices utilizing the Johnsen-Rahbek effect still exists.